Electronic paper, also referred to as e-paper, is a type of an electronic device that can play a role of paper because, just like a paper book, a newspaper, or a paper magazine, one can readily carry it around and conveniently read and make notes on it whenever one wants.
Such electronic paper may take a form of an electrophoretic display, which is advantageous in that not only is it flexible enough to be bent, but it can also be produced at a much lower cost than conventional flat panel displays and is far superior in energy efficiency since there is no need to furnish an additional backlight. The electronic paper shows high definition and a wide viewing angle, and may have a memory function such that the letters displayed thereon will not disappear completely even in the absence of power sources.
Such markedly advantageous characteristics of the electronic paper hold great potential for a wide variety of applications such as an electronic book having a paper-like plane and a moving illustration, a self-renewable newspaper, a reusable paper display for cell phones, a disposable TV screen, and electronic wallpaper, and its latent market surely seems to be huge. Depending on the realization method, the electronic paper can be typically classified into an electrophoresis type, a liquid crystal type, a toner (QR-LPD) type, a MEMS type, and the like. Among them, the electrophoretic type is based on electrophoresis of charged pigment particles suspended in a dielectric solvent. When a voltage is applied across the electrodes being opposite to each other, the charged pigment particles are made to migrate toward an electrode bearing a contrary charge to that on the particles by attracting forces, thereby expressing a color or light and shade.
Among such electrophoretic displays, the microcapsule type and the micro-cup type technologies, which are most likely to be commercialized soon, take advantage of particles as a color display element. The microcapsule type of electrophoretic display is a display device wherein a dispersion including charged particles and a flowing fluid is encapsulated in a microcapsule and placed between the opposite electrodes. The micro-cup type of electrophoretic display is a display device wherein a recessed unit as defined by a partition between the opposite electrodes has charged particles or a slurry of charged particles enclosed therein.
However, the electrophoretic display devices hitherto known have failed to sufficiently show color reproducibility or contrast to be actually applied in various fields and did not secure appropriate reactivity to a driving voltage and a capability of appropriately maintaining an afterimage when the driving voltage is eliminated.
In addition, the electrophoretic particles are typically used in the electrophoretic display device as they are dispersed in a flowing fluid, but the electrophoretic particles hitherto known often fail to be stably dispersed in the flowing fluid, resulting in the formation of agglomerates. Moreover, the electrophoretic particles of the prior arts tend to be partially dissolved in the flowing fluid or absorb some of the flowing fluid to swell, showing changes in their properties or true specific gravity themselves, and this can even lead to a decrease in contrast or response speed of the electrophoretic display.